Why would a man be interested in your family?

So I have a guy who has always been just a friend to me and I've always slightly liked him more than that. But everytime he hears someone with my last name he has to go up to them and ask if their related to me. He knows my siblings and my parents and yet he doesn't like me that way to want to know my family. Like he's not my boyfriend but introduces himself like he is.
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Another thing why does it matter who's related to me to him? Especially if has no interest in me romantically.
Why would a man be interested in your family?
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